Evaluating the effects of Caspian Sea water level fluctuations on the coast morphodymanics (Case study of Spit Miankaleh and Gorgan River delta)

The changes in the water level of the Caspian Sea cause many problems in the field of sustainable development of the coasts of this lake. The Caspian Sea water level fluctuations are severe and has varied between -۲۵ and -۲۹ meters between ۱۸۸۰-۲۰۲۳. The short and long-term planning of the countries along this lake depends on comprehensive understanding the effects of these water level fluctuations on the coasts, and any planning to achieve the desired regional goals will fail without paying attention to these processes. The aims of this research are evaluating the effect of sea level fluctuations on the Iranian eastern coasts of the Caspian Sea from Amirabad to the Gorgan River delta and to determine the vulnerable areas of the coasts and also assessed the effect of these fluctuations on the hydrodynamics of waves. Hence coastlines extracted from Landsat data in four time periods of ۱۹۷۵, ۱۹۹۸, ۲۰۱۱ and ۲۰۲۳, besides DSAS system was used to quantitatively evaluate the rate of changes in coastlines. Also, MIKE۲۱ software and sea buoy data were used to investigate the effect of sea level fluctuations on wave parameters. The results indicate that the mouth of Gorgan Bay and the Gorgan River delta where the most unstable parts of the coastline and are highly sensitive to sea level fluctuations. Between ۱۹۷۵ and ۲۰۲۳ more than ۴۶۰۰m coastline changes observed in this region, especially in the Gorgan Bay mouth. In addition, the results of the modeling of wave in high and low water table show that the wave height has increased simultaneously with the rise of the sea level, and the maximum wave height has increased from ۱.۳ meters in ۱۹۷۵ to ۱.۶ meters in ۱۹۹۸, this increase in wave height besides submergence of coastal areas can intensified the process of erosion in the coastal zone.